Well, I don't really quit when having a losing streak. I might take a few days off, but in general I am more slowing down a bit and that would be my advice.

Discipline and money management are two big key ingredients, when it comes to professional gambling. If you lose your mind easily in tough situations, this might not be the right profession for you. Tilting has already seen a lot of bankrolls being busted and you better not have a tendency to go on tilt when gambling.
Don't question everything that worked before just because of some variance and keep looking at the big picture. This is pretty general advice, but it's a psychological issue in the end and each person deals differently with it and has to find an individual way to turn things around again. There is no golden way nor any magic pill.

A good and proven money management will help a lot in these situations. It will automatically lower the stakes while on a losing streak and you should even lower the stakes yourself (in addition to your money management telling you to do so). So instead of flat-staking lets say 1.5% of your bank, you can go down to 1% or even 0.5%. Start small again to get your confidence back, you can always up your stakes at a later point again. But during a losing streak you have to protect your bank first.

And as I said earlier somewhere in this thread, you should also have some backup money in place. This should be enough to cover your expenses for around 6 month without winning anything from gambling. This will give you some mental peace, since you know whatever happens, I am safe for the next 6 months.