Q.crepe myrtle branches flopped to ground
It is two yrs old, not dead at all, just flopped to ground with its flowers. Do I cut tree back low? Please advise. Thanks.

Improper pruning can result in Crepe murder.
Read the links below to determine how and when to prune.
Can you remove a few of the blossoms to lessen the weight on the branches?
I would take this approach for now and then work on the appropriate pruning technique.
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-care.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm