You have to use same .jks file that you have generated first time when you want to generate Signed apk.
Use .jks name same as created first time like key0 do not change it to key1.
Once you created .jks file and upload the apk to playStore , No need
to create again , use same .jks every time. If you create .jks file
again & used new .jks then playStore will not accept your .apk .
Only need to change in build.gradle(Module:app) :
you have to increase your below both every time when you want to
upload apk on playstore.
versionCode 2
versionName "1.2"
Reference : https://developer.android.com/studio/publish/app-signing.html