How can I make fields only accepting numeric values?

Are you asking to have your field accepting only numeric values?

You can:

Doing so will make that field like this: 

Or you can also use the Number field from Quick Tools of the side panel of your Form Builder.

This automatically required form-submitters to enter a number. Entering a number from the keyboard will not make any effect at all (or there will be no input written on the field if it is not a number).

I hope this helps. Let us know if you need any further assistance. Thank you.