Then the character impresses the king and court that he really can serve excellently well as a knight. And even knows a trick or two about their perpetual warlock foes that the current crop of knights didn't know.
Notice the vacuity of that. He could kill a bear, he could break a curse on a forest grove, he could fight some knight who proved, after defeat to be nothing but a suit of empty armor. Details aren't important.
Except that of course they are important because they are needed to convince the reader that he really does impress.