After Battery Replace only apple logo comes on

The iPhone 8 doesn't require any special tricks to replace the battery so a replacement should just drop in and work. Obviously something went wrong somewhere along the way.

First thing to do is to see if it charges wirelessly. If it does, chances are the lightning port assembly got damaged and will need to be replaced.

Otherwise, open up the phone and check your work. In particular check any of the display and battery connectors that were unplugged in the process of the repair. Use a magnifying glass and a bright light and check the ribbon cables for any tears, and the connectors on both sides for bent or broken pins. If everything looks good, clean the connectors with 90% or higher concentration of isopropyl (rubbing) alcohol and reassemble the phone.

Recheck to see if it's working. If not, try swapping the old battery back in - there's always a chance you got a defective part. If the old battery works, you'll need to get a replacement; either contact the original seller for one or just buy another one from a different vendor this time.

Try out those suggestions then come back and let us know what you found and we'll figure out what your next step should be.