As mentioned before though, a lot of men get into this because of and can't commit to the act due to the mental aspect. And this can take some work.
1. Read, look at or watch porn and erotica about men eating cum and figure out what turns you on the most about it. Is it the idea of being dirty and kinky? Is there a punishment or humiliation aspect to your desire? Do you see others get pasted, and long to feel the same sensation?
2. Dive into that desire. Don't forget how silly sex really is, and understand that vulnerability is the whole game. So if you need to role play with a partner or by yourself, talking dirty and hyping up the act- just fucking do it. You're not guzzling cum with the Queen here, so if you need to berate yourself into doing it, calling yourself names- do it. This should be all about shedding inhibitions.
3. Train. You've essentially been doing cognitive behavioural therapy your entire life just to act proper- so don't be hard on yourself trying to get a little primal. Watch your favourite creampie eating porn, understand your desire and practise getting into the headspace. Some folks may be able to just jam their slick fingers in their mouth, but many others need the time to get there. If that's you try and enjoy the slow build and don't be too hard on yourself.
Hopefully I've given you men some helpful advice to be the cum guzzling freaks you've always wanted to be.
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As with any and all advice on sex acts you might find online, remember that these are fun and playful suggestions from strangers and things written here in no way supersede medical advise from trained doctors and nurses in regards to personal health and well being.
Educate yourself on STIs and disease prevention, and try your best not to use sex as a self-led therapeutic practise. Submissive roles and denigrating practises during role play can be fun and sometimes helpful, but can also be triggering and traumatic for those with negative experiences and mental health issues.
Experienced doms and subs are hopefully versed in and practise healthy aftercare as well as solid two-way communication about boundaries and consent.
I think that's as responsible as I'm going to get now, please play safe, love yourself and stay kinky!