Write the seven letters of the scale under 1 to 7. Then leapfrog: a chord is a number, the number two above it, and the number two above that. Past 7, carry on from 1. So I is 1 3 5 and vim is 6 1 3. Write the letters inside each chord, then play it.
Nothing about the numbers has changed. Only the letters under them.
Keyboards: try F or D. Guitars: D — D, A, Bm and G. Which chord was new to your hands?