It won't do the tyre much good (or the handling) if the tyre isn't seated on the rim correctly. So you need to deflate the tyre and probably add some lubricant between the tyre and the rim, and then re-inflate it but don't overdo it. Up to about 20% over the maximum running pressure is advisable.
Proper tyre fitting lubricant or paste should be really be used, but some owners use washing up liquid, Swarfega or even WD-40, but I wouldn't use those myself except in an emergency, maybe, as washing up liquid can cause corrosion inside the rim? Liquid hand soap is better.
Also check that the insides of the rim aren't corroded, as a rough, rusty surface can prevent the tyre from seating on the rim properly. Most tyres have a moulded line near the edge of the rim? If the line is the same distance from the edge of the rim all the way around on both sides of the tyre, then the tyre should be sitting on the rim correctly?