General wisdom is that if you feel unwell above the neck (blocked nose, sore throat, headache etc.) then it's probably fine to work out. If your symptoms are below the neck (temperature, muscle aches, tight chest etc.) then it's probably best to rest. Given the covid situation, I imagine it's best to err on the safe side and rest (although I'm not a Dr!)
From personal experience, I usually find I feel better after working out. But if my symptoms got worse after I started to exercise, I'd probably call it a day.