Betta Fish: Help with parameters

I was finally able to get a liquid test kit and my ammonia nitrite and nitrates all seems high (the ammonia test looks slightly more green in person but its likely in between 0 and 0.25 ppm). I initially tested last night and the nitrites looked an even deeper purple so I did a 25% water change last night and the nitrites have slightly gone down. My lil guy seems to still be doing fine, swimming around as normal.

What can I do to bring the levels down quickly? I’m assuming more water changes – but how often is too often and how much water would you recommend? Is there anything else I can do?

I feel so bad cause the levels seemed perfectly fine on the test strips – goes to prove how inaccurate they are!!