Miliput, green stuff or similar.
Roll out a small 'ice cream cone' & attach it to the flagpole with a spot of superglue.
Leave it for about 5 minutes. That will let the superglue set & not stick to you when you put in the creases to the 'flag' (use a cocktail stick)
When you are happy with the effect, use a craft-knife to create the fringe (if you want one)
Put it to one side & leave it overnight to set solidly. You might want to give it some more superglue to ensure it all stays together.
Next day, paint it. Remember you are NOT trying to replicate the flag details fully. Suggest details. Most detail would not show & it is in 15mm.
I hope this helps.