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If you already put down seed, without any soil preparation, getting the new grass to grow well is going to be difficult. Work at improving the health of the soil as an ongoing project. Organic lawn fertilizers can be used to build soil fertility in addition to providing excellent nutrients to help the grass. Be aware that these natural fertilizers can take longer to show results when the soil temperature is cooler.

Silverfish are attracted to paper and clothing; dark and damp is there happy place.

Look for traps or insecticides that treat these pests.

This may be a fungus called, Gaeumannomyces fungus.
This link may help you.
https://ask.extension.org/questions/182264

High nitrogen levels can burn plant roots. Your best bet is to water the lawn heavily and get the nitrogen to move through the soil. It is impossible to say whether the grass will recover. This fall, do a soil test. Potassium and phosphorus move very slowly through the soil and can build up to toxic levels. In addition, many US soils have sufficient amounts of phosphorus naturally and phosphorus is a big pollutant of waterways. On the market now are lawn fertilizers with only nitrogen and potassium (potash) as well as nitrogen only fertilizer. Soil test results will guide you regarding the lawns fertilizer needs.

These links will help you choose the correct grass.

https://www.gardeningknowhow.com/ornamental/trees/tgen/tips-for-growing-grass-under-a-tree.htm
http://ucanr.edu/sites/sjcoeh/Turfgrass/Choose_the_right_grass/