Get the tyre seated on the rim correctly making sure you don't have high spots etc. Once everything looks OK, peel back the tyre slightly until you can see the bead and run some superglue in the channel that the bead sits in.

You won't need much 'cause it runs round the rim. I do this at 4 points round the rim on either side.

Each time you put the glue in, be sure to re-seat the bead of the tyre in the channel of the rim carefully.