I have a snapper sz2042 zero turn and I’m having steering issues. It will only turn right. It will turn left but only at low speeds. How do I fix this. I’ve looked and I can’t find anything online that says how to adjust it. Thanks

How does the drive belt look?  If it's worn it can cause slipping.
Also, any oil leaks, from the engine onto that drive unit, WILL cause slipping.
 
I would check and make sure all of part #10 is not stripped out/loose:
https://www.partstree.com/models/sz-2042-2691571-00-967947601-snapper-42-zero-turn-mower-20hp/transmission-group-2/ 
 
Re adjustment (likely does not need it as it's been fine), parts 9 and 10 can be adjusted:
https://www.partstree.com/models/sz-2042-2691571-00-967947601-snapper-42-zero-turn-mower-20hp/steering-group-5/ 
 
Lastly, I'm not sure, part # 8, an idler pulley is part of the drive system:
https://www.partstree.com/models/sz-2042-2691571-00-967947601-snapper-42-zero-turn-mower-20hp/engine-mounting-group-1/   
In any event check it, make sure it spins smoothly and also that the drive belt from the engine to the hydro's is tight (should have some spring tension on the single belt..
 
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