Looking for some advice about re-applying.

Here's a bit of background; so when applying for uni this year I knew I wanted to go to uni in Sheffield to do sociology. I got offers from both Hallam (unconditional) and Uni of Sheffield (conditional BBB), however when putting my first/insurance choice, I had so much self doubt and didn't for a minute think I would get BBB. However, I did. I'm currently taking a gap year to go travelling/earn some money before I go, however I want to reapply to sheffield uni of, but ive got the confirmed place for hallam in sept 18. I missed the adjustment period so im unsure of what to do now, will i have to create another ucas account or is my best bet just to phone the university.
conclusively im an idiot, hope someone can help with what i can do next,

Email the undergraduate office for Uni of Sheffield (or your department) and tell them that you had an offer from them, would like to go there next year and whether they will reconsider you. They'll probably ask you to make a UCAS application for logistics but I imagine they'll give you an offer again