Clean a shirt

I’am a Barista work 10 hours/day, in a Bar in London.
During my job, I have to wear a formal shirt. but the problem in the end of my shift, I have Collar Stains,in my arms too. ‘pity this shirt is too expensive and I have to wash it at home’
This week, i WASHED my shirt, but still dirty in the collar. so What’s the best solution to get washed my shirt and clean 100 per cent ?