Looking for advice: started job & now want to leave

for context: I had a job that was working great remotely but became less consistent. I began looking for and secured a part time job that I dreaded from the beginning. It’s far, I have to uber which is expensive, and they are not paying that well. After one session of training, a few weeks ago, I tried to resign because I found out I’ll need surgery. They insisted they’ll hold my spot until I return and I said okay, thinking that I will still need a job. In the past day, I secured another job and am not sure what to do with the dreaded office job that is expecting me to return tomorrow. Do I give the manager a heads up I’ll be resigning? I haven’t even trained really so I’m not sure whether it’s valuable to go to the office and share my resignation (+ the offer of finishing the next week & attempting to help them find another candidate for the inconvenience) or if I should call today and resign? I know of course I got myself in this spot and am going to suffer with the consequences but I don’t know how to approach this.