Take your shot as soon as you remember about it. Tresiba is a wonderful insulin in this regard, its cycling will not lead to either hypo or spike if you give an injection a few hours later. I do not advise repeating my experience, but even after 12 hours everything was fine
We can't advise on dosing but this is the information in the UK leaflet:
My own experience is the same as @Zhnyaka 's. I once forgot to bring my Tresiba for an overnight trip so I took it about 15 hours late without ill effect.
Basal compensates for the work of the liver, it has nothing to do with how much insulin you need for food. You will either have to compensate for the work of the liver with a bolus, regardless of whether you eat or not, or you will not have to do anything (tresiba is usually the second option, it can be injected at any time of the day)