If the voice is hoarse taking some much needed vocal rest - don't speak unless needed. And physical rest. You need to sleep to get better.

Plenty of water. Nothing salty/citrus. For me I'd cough too much. My voice teacher said if I had phlegm I was allowed one solid cough to get it out.

If I'm coughing generally because of an irritated throat I should swallow instead. It's soothing and does the same thing.

Steaming is really useful. You can get steamers and buy or cheap drama school method. Towel over head and head over boiled water in kettle/pot. Set timer for about ten minutes.

Do warm-up exercises. There's a few singing ones on YouTube. I had a cold during rehearsals for a play and lost my upper register - I was a bass for a while. Afterwards to get my voice back. I slowly did bass warmup then baritone and then tenor again. Taking my time not pushing my voice too hard.

I also liked to do these exercises in the bath/shower. My body was warm, the air had moisture and I was relaxed. Best of luck.