Work out and lift weights. But ergonomically speaking I use a Kinesis Advantage 2 keyboard and a Logitech MX Vertical mouse. You may also need a long break to heal, which might not be an option if you're American. An engineer from Germany I know had something like 4 or 6 weeks off work when diagnosed with RSI and nobody batted an eye.
I got the MX Vertical, K860 keyboard, All33 Chair and it has been amazing for the pandemic. At work I had crappy Dell keyboards, a basic mouse, and a horrible chair. It's night and day. Changed my monitor from a crappy monitor to a high DPI monitor and it's so clean and great for your eyes. Granted, all this can be alleviated by working out and sunlight. Get those bands and just work out. Nothing beats it.
My best advice. Try everything and see what helps. I’ve tried every keyboard under the sun. I even bought a datahand keyboard. The Kinesys Advantage is amazing. I have one. It made the biggest difference for me. I cannot use a mouse anymore not even for 10 mins. I use a touchpad now but in the beginning a Wacom touch pen (you can configure it to work in mouse mode) was the only thing I could use. Try these things and see what works.
A physio also gave me some writs stretching exercises to do each day which helped a little.
Biggest things that helped me when coding?...
Kinesys advantage keyboard
Wacom Bamboo tablet and pen (with mouse mode). It’s odd a first but seriously try this if you can’t use a mouse.
Highly recommend trying this.
Ps. Take it seriously and don’t just plough through it. It might never go away fully but you can avoid it getting so bad it affects your career.