This will extract the first name:
=LEFT(C6, FIND(" ",C6)-1)
and this will extract the last:
=MID(C6, FIND(" ",C6)+1,100)
Of course it will only work if there is one first name.
If I understood what you want you can use:
First name: =IF(ISBLANK(F3), F3, LEFT(C6, FIND(" ",C6)-1))