[AC Question]

This is an LG Android smart phone.

[anon8380037]

Do you mean on the Gmail app. If so, hold on one until a grey top bar appears which will have icons including a trash bin. Now you can hold more to delete and a count will appear. When you tap the trash bin it will ask if you want to delete said number of emails. When you do, an Undo bar appears at the bottom for a short time.
If the LG email app, I don't have one, but imagine it's something like menu - select, then delete.