There is a presser foot called "Darning foot" - for that machine. It came with the machine and should be in the accessory box.
Then look for "Darning with straight stitch" in your manual for how to put it on. Read the instructions very very carefully. It's a bit of a challenge to get it on correctly. You will probably have to go through the manual page by page to find it.
(The manuals for the Pfaff 1471, 1473, and 1475 leave a lot to be desired as far as their indexes/table of contents are concerned)
Have you been using that foot?