Speedometer Re-Calibration After New Tires

[Cadillac Kid]

Hello.

I recently went from the 235/75r15 tires that were on my truck to 31x10.50r15 tires. They are taller, and because of that my speedometer reads slower than the truck is actually going. I don't know what speedometer gear I need to change to. I'd think that someone has had this issue before after installing taller tires. Any guidance is appreciated.

Thanks

-Gavin