Question Cpu frequency drops

[FluffiSup]

Please help I was recently cleaning my laptop from dust and I removed heat sync and cleaned the fans then I assembled it again. Everything was looking fine until I turned on a game and it went something like 5s 70fps and then drop to 3 for 4s and again. I looked into it and saw that my CPU went from 3,5GHz to 0,7-0,8GHz. I don't know if I damaged anything.
Before I cleaned my PC I was using undervolting and games ran fine but after I cleaned my pc it is a lot cooler but games run worse temp. before: 70-90C after: 40-55C.

I have a laptop Acer Nitro 5 with:
Intel Core i7 - 8750H
2x 8Gb ram both 2400MHz
GTX 1060 6Gb VRAM

 

[sizzling]

Did you clean off the old thermal paste and replace with new?

 

[FluffiSup]

No, I didn't replace thermal paste