Tyre has a 'dip' in it after fitting to rim
I used to get this a lot on my old 29er with Continental commuter tyres, large rim with tight tyre made for tough work getting the tyre on and off and often got similar flat-spots.

Check the max psi first but pumping up as hard as possible can ping the tyre beading back on to the rim wall, then deflate back down to your proffered pressure. If its still reluctant you can buy rim lube type stuff (could be a risky Google that, sorry) which is basically washing up liquid, so try that. Add a bit around the tyre wall / beading while its off rim and it will help ping on when you pressure up the tyre.

Track a pump will be your friend here.