Authorizing myself to get to the weight I want

I am 5’7 and weigh around 135-140. I want to get to 120 lbs which is the weight I know I feel my best and can wear the clothes I love (I have a true passion for clothes). However, I have a huge desire to overeat and my brain keeps telling me that I will never get there and go the “extra mile” and that I should just settle and satisfy myself with what I have – I then slip into complete apathy and go “since I’ll never get there, might as well eat”. Any tips to “authorize” myself to choose 120 lbs as my goal weight and to get there? Thank you so much, as always!