For freya or Freja that the swedish spelling goes have to my knowledge not a seal as we would have for the 72 demons in goetia.
The simple way would be to use the runes from the Futhark to spell her namn then combind those runes to a singel seal or bindrune and use that. The way you combind the runes should be a way that your intuition helps you with, the 2 different ways i would chose among is,
1 stack all the runes ontop of one another which would give you one ”single” Rune in the end.
A more traditional way is to make a sort of bindrune in essence you combind the runes from the namn to one bigger symbol.
The first method enda up with a symbol the normal size of 1 rune the second method gives a bigger symbol that more would look like what most of us would consider a seal.
So do whats up to your own liking.
Did an example for it for the fun of it.
The top is the spelling of frejas name, the second raw is the runes stacked where i try to align them a little to not make to big of a mess with it and the third image is a little more seal type inspired combination, The lines for all the runes are in the symbols.
Now the number 3 is important in norse viking magic aswell and with the runes so another level would to make a seal typ symbol but trying to combine the symbol 3 times.
Take my 3 one for example you could copy it 2 times and add it to the fist in nice 120 degre angles and get a nice seal that way.