Named args of a function

I have a function with named args:

f1(a1; a2=1, a3="a")

I have the Symbols :a2 and :a3 but this does not work:

f1(a1; :a2=1, :a3="a")

Given the symbols how do I assign a value to the named arguments of f1 in the function call?
Thank you

Obviously I can’t write directly:

f1(a1; a2=1, a3="a")

because I got the symbols from another function

I think you want

f1(a1; :a2=>1, :a3=>"a")