Trouble figuring out [H+] and [OH-] on a calculator

I tried to calculate [H+] and [OH-], I understand the concept of it and how it goes but I have trouble with realizing how it goes on my calculator. So far I tried

1. puting the value of pH/pOH (that comes to a decimal number) in the calc but it doesn't support it and it doesn't even allow me to press . when I am typing the number, it only works with the whole numbers

2. I tried to solve it using math by hand, but it's complicated for me and I ended up more confused.

3. I searched on yt and Google the how-tos for my calculator but I didn't find anything. I even read the manual but it never mentioned when the number on the power is a decimal one.

Did anyone have a similar problem? How could I calculate the number?

My calculator is Citizen SR-260N.