When you notice you are being critical of yourself, beating yourself up or putting yourself down, notice the words you use, the tone of those words and really notice how they make you feel - do they make you feel worse or better?
Then ask yourself, 'what would I be saying to a friend/someone I care about right now?' 'would I be talking to them in the same way?' 'what would be different about the way I talk to someone I care for or love?'
Notice what different words you would use, what tone you would use and be curious about how that makes you feel
See if you can start practicing talking to yourself in the same way you would speak to someone you love and let me know how you get on.
This isn't always easy and won't be a magic fix that makes you suddenly stop criticising yourself! BUT practicing noticing HOW you talk to yourself can help you become more curious about where your negative self-talk comes from and more aware of those unhelpful cognitive patterns.
If you want to target this further my therapy approach can help you identify what's underlying your self-criticism and how best to implement long-lasting changes to unhelpful cognitive and behavioural patterns.