Open the settings of windows terminal (you can also use ctrl + ,).

At the "Actions" Tab, you can set (if it didn't) the keymap for resizing pane, in my setting it is set alt + shift + [direction], change the [direction] with right, left, up, or down arrow.

I also often to use Toggle Command Palette by pressing ctrl + shift + p then search for the keyword such as resize if I forgot the keymap. I can't post the image because of reputation restriction. I hope it could help.