I had issues with my dad. he was horrible. He destroyed me as a young person and set me up to fail. He sabotaged my attempts to succeed. He was not a nice man. But I try to forgive. He's dead now. I try to understand where he was coming from, try to understand his point of view. I wrote about it when he died. I don't know if you can relate. I'll share the link.
It's not the same as a work colleague who perhaps you have less reason to forgive, but frankly, work colleagues are not worth your time. Try to focus on other stuff and maybe your feelings will just go away. There are all sorts of things that I feel resentful over if I think about them. I try not to think about them. Anyway, here's my dad....
https://medium.com/illumination/my-dad-died-this-morning-af36244ebf31
And this...
https://byrslf.co/i-slowly-watched-my-father-die-2549afc45ab2?gi=d5159944c5fd&source=post_page-----af36244ebf31--------------------------------