What's your question? Ask

There are a number of reasons for yellowing leaves in plants. This article should help you pinpoint the most likely cause for yours: https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm

Since I, personally, don't recall seeing your question before, I can only apologize to you that you didn't get the information you needed when you asked earlier. I'm going to say some general things about dieffenbachia, and if they don't cover your problem, please feel free to write to me personally with your question. This article might address your situation: https://www.gardeningknowhow.com/houseplants/dumb-cane/growing-dumbcane-dieffenbachia.htm
The problem most likely to afflict dieff is root rot from soil that stays too wet. Testing the soil moisture in the bottom of the pot will remedy this. You can use a moisture meter, or a wooden skewer as if testing a cake. The soil should be very slightly damp before you water again.
If the roots have been damaged, move the plant into higher light to promote increased water evaporation and root growth.

Hopefully, you put it back into the house when you saw the leaves starting to burn. There's nothing you can do to "save" the damaged leaves. When plant tissues are dead, they're dead. However, the plant itself should be okay, and it time will put out new leaves, if cared for properly. Cut off the damaged leaves at the point where the leaf stem is attached to the main stem. Keep the plant in bright indirect light in your house - anyplace that you can read comfortably. If you want to put the plant outside for R&R, it needs to be in heavy shade. Indoors or out, you need to be careful to not overwater - the soil in the bottom of the pot should be very lightly damp before you water again. A moisture meter that you can get in any plant store or dept will help you alot.

Here's more information on dieffenbachia: https://www.gardeningknowhow.com/houseplants/dumb-cane/growing-dumbcane-dieffenbachia.htm

Make sure your providing adequate light for your plant, bright filtered light is required for most Dieffenbachia. Plants should be rotated to insure even growth.
You can use a process called air layering to start new growth on the stems, or you could propagate new plants from your mother plant.
Here are some links to help you get started.

https://www.gardeningknowhow.com/houseplants/dumb-cane/growing-dumbcane-dieffenbachia.htm

https://www.gardeningknowhow.com/houseplants/hpgen/propagating-runners-on-houseplants.htm

https://www.gardeningknowhow.com/houseplants/dumb-cane/propagating-dieffenbachia.htm

The pot looks quite large. You mention watering once a week. Do you check by feeling the soil if it is wet, or just water every week?
I think the plant may be waterlogged. I would recommend repotting into a smaller pot.
A good filtered light near a window would be a great spot for your plant.
After repotting you could fertilize the plant to help it get growing again.

Here is a link with great growing directions.

https://www.gardeningknowhow.com/houseplants/dumb-cane/growing-dumbcane-dieffenbachia.htm

When did you bring your bring your plant outside? I am just wondering if possibly it got nipped in the cold at some point? Also, when you brought your plant outdoors, did you immediately put it in a location of full sun? Some dieffenbachia plants require low filtered light - so it needs to be in a shady location. Your dieffenbachia probably found its new setting a lot brighter than it’s accustomed to inside your home - it could literally get sunburned. Ideally, indoor plants should be slowly acclimated and transitioned to outdoor life. Here is an article on acclimating houseplants that will explain more:

https://www.gardeningknowhow.com/houseplants/hpgen/acclimating-houseplants-outdoors.htm

For more information on the care of dieffenbachia, please visit the following link:
https://www.gardeningknowhow.com/houseplants/dumb-cane/growing-dumbcane-dieffenbachia.htm