Okay so that's good news. It's high, but I've seen sky high nitrates out of the tap which makes for a real challenge.
Simple answer is water changes. Lots of them. In my opinion / experience...there is no such thing as too many water changes as long as you're using conditioned, temp matched (at least close) water.
I've had aquariums for the last 20 years, and it's a religion to do a 50% PWC
at minimum once a week. Hell, I'd do them daily if I had the time and willpower
For simple math, start by doing large enough and frequent enough changes this week to get down to your baseline out of the tap. From there you'll have to decide if you're able to keep up the water change regiment to keep nitrates at or below 20ppm, otherwise start looking at options like planting with nutrient hungry plants (plant experts here could give you recommendations...Water Sprite comes to mind), otherwise running media in your filter to absorb some of the nitrate. I'm not a fan of chemicals personally, but it's an option.
If you're up for the challenge, plants combined with frequent PWC
's is the best option, but if you haven't done a planted tank before make sure you do your homework. They're amazing, but definitely add another dimension which takes time and energy.