Can I disconnect battery cable while the iPhone 7 is on

You can disconnect the battery from the phone and it won't hurt it. Just don't disconnect the screen until the battery is disconnected. Changing the screen will not get rid of the apple logo. It's in a boot loop. It most likely has a problem from water damage. The problem is once they are wet they have problems for the rest of there lives IF you can get them working again. Most repair shops won't even work on them except to retrieve data when they are water damaged. If you want to try to fix it you need to pull the board out and remove the covers and see how bad it's corroded. Save the covers for the chips in case you can get it working. Once it gets wet it starts corroding and it does it faster if it has power connected to it. Did you try to charge it after? The first thing you should have done is open the phone and disconnect the battery and pull the board out and remove the covers on the motherboard and dry it off with a heat gun or hair dryer. Then clean any corrosion with a qtip and alcohol. See how bad it's corroded and you might try cleaning the board and see what happens.

So I accidentally disconnected the screen before disconnecting the battery now my phone won’t turn on prior to this I replaced the charging port it turned on but my touch sensor wasn’t working so I disconnect the screen instead of the battery first what should I do I have a fresh screen coming in within a couple days but I’m worried that my battery is screwed or my board in general please help