The Erase Alpha brush mode basically paints the alpha channel of an image black. Add Alpha paints it white. Black means the model is transparent at this spot. The image must have an Alpha channel (RGBA).
You can view the alpha channel if you connect it to an Emission node as show in the screenshot below. The Node Wrangler add-on can do this automatically for you with Ctrl+Shift+LMB.
If you set the Blend Mode in the material setting to Alpha Hashed you should see the hole in Material Preview and Eevee render mode. The render engine must be set to Eevee to see the setting.
If the setting is not correct the spot will not be transparent but shown as black.
With the Add Alpha brush mode you can fill the hole. In in Image Editor on the left you should see the transparency. The image must have an Alpha channel, of course.
To remove the bumpiness of a bump map just paint the image with the grey color 808080 (HEX). Make sure the Color Space is set to Non-Color.
The image must not be transparent at that spot.
Brighter values up to pure white will create a bump while darker values will create a dent. Use the Mix brush mode.