If you only have an OTO tester (yellow color) then I would not swim if the color is orange (shock level) or brown ('nuked' pool
) If the color is darker than your darkest color block but still yellow you can swim since your chlorine is high but not THAT high, probably only up to about 10-12 ppm.
You can get an estimate of how high your clorine is by diluting your sample with distilled water. use a measure like a shot glass and mix 1 part pool water and 1 part distilled water, test and multiply your test results by 2 (so if your test indicated 5 ppm then it's really about 10 ppm).
If that is still not high enough then mix 1 part pool water with 2 parts distilled water and multiply the results by 3. If you neeed to go higher it's 1 part pool water and 3 parts distilled water and multiply by 4. The highest I would try and go is 1 part pool water and 4 parts distilled water, multiply results by 5 because each dilution reduces the accuracy of the test so the higher dilution tests are more of an estimate of your chlorine.
It is generally considered ok to go in a pool when the chlorine is below 10 ppm (there are a very few special cases where it's ok to go in when the FC is higher but we are not discussing them here so stick to the 10 ppm number.)
Shocking won't lower CYA. Only doing a partial drain and refill (or a series of them) will.