Adjustment uni help: changing course

I applied for chemistry at Southampton but have changed my mind and now want to do natural science.
I have received an offer from Southampton to change my course, I've verbally accepted the offer and reciceved a confirmation email however it hasn't appeared on my UCAS. I've rung them and the girl that I spoke to filled out a request form and said I should get an email with what to do (haven't yet)
I'm kind of panicking and unsure what I need to do now, all the UCAS guides say not to decline the offer I already have and that the uni should just be able to add my new offer onto UCAS track that I can then accept on there, but one of the people I spoke to said to decline the offer I had.
I'm really worried I'm going to miss out on the offer and don't know if I need to do anything
I don't really want to decline because if I don't get the other offer come through I'll just take the chem course

Any advice would be greatly appreciated 🙏

If you have gone through Adjustment your firm choice is not at any risk, and the uni needs to do the update. It's only if you need to go through Clearing that you decline an offer. Southampton probably just need to go through and change your course choice option

Ok thank you so much, I guess I'll just have to keep waiting for it to come through but it's really good to know that I don't have to decline it/it's something I've done wrong

I know the wait must be nerve wracking! They are probably still busy sorting out Clearing applicants too