How do I empty Mail Trash in iOS 13?

Hello jsbsvb123.

Welcome to Apple Support Communities.

If I'm understanding correctly, you need some help with deleting multiple emails from the Trash folder in the Mail on your iPhone. I will be glad to assist.

Please see below from the following resource:

How to delete emails on your iPhone, iPad, and iPod touch

"How to delete emails

To delete a single email or multiple emails:

1. Open Mail and go to your Inbox.
2. Tap Edit in the upper-right corner, then tap Select All. Or individually select the emails that you want to delete.
3. Tap Trash or Archive.

You can also quickly swipe left over a single email to delete it. To undo deleting an email, shake your device, then tap Undo.

Depending on the type of email account you have, you might see Archive instead of Trash when you try to delete emails. You can edit your mailbox behavior settings to change this."

Cheers.

If your email account is a Gmail account, follow these steps:

Go into Settings / Passwords & Accounts / Gmail account

Tap on the account (e.g. myname@gmail.com)

Tap on Advanced

Under Move Discarded Messages Into, tap on Deleted Mailbox

Tap on Account at the top left of screen

Tap on Done

Tap on Accounts

Close Settings

Close the Mail app if it was open

Reopen the Mail app and go to any of your Mailboxes, click Edit and then Select All and you should see at the bottom - Mark, Move, Trash (or Delete)

It's important to close out of Settings and the Mail app for the changes to take affect.