delete text messages from iPad

My mistake - but exactly the same process applies for deletion of Messages from the Messages App…

At top-left of the Messages sidebar, tap the Edit button then Select Messages from the menu. Swipe your finger down (or up) the left-side of the sidebar conversation list to bulk select Messages. Swipe below the bottom edge to rapidly select (and scroll through) all the visible email messages.

Once selected, tap the Delete button at the bottom-right of the sidebar.

If needed, start by searching your mailbox by Sender or suitable keyword - and/or combining with a filtered view in the Mail App sidebar:

Flag and filter emails on iPad - Apple Support

Next, tap the Edit button at top-right of the Mail sidebar; simply swipe your finger down (or up) the left-side of the message list to bulk select Mail Messages. Swipe below the bottom edge to rapidly select (and scroll through) all the visible email messages.

Once selected, tap the Delete button at the bottom of the sidebar.