Fingering of one particular moment depends on what comes before and after. There isn't one correct fingering. So, you need to have a rationale for your fingering choices. I did this as my first thought...
Generally you want to make fingering changes to place new fingers on adjacent keys or substitute new fingers on one key, because once a finger is down on a key it's fairly easy to place another finger on an adjacent key or make a finger substitution. By comparison, if you lift your whole hand off the keyboard, you loose the spatial point of reference of an already placed finger and it harder to hit the target keys.
5 1 is just a 5-finger position on a perfect fifth, then
5 3 involves crossing the thumb under and placing finger
3 adjacent to the thumb on the
G# key, then
2 1 just involves placing finger
2 adjacent finger
3 on the
A key. Each of those moves involves and easy, adjacent placement of fingers.
The problem I see in the SimplyPiano fingering is all of the moves involve a lift of the thumb.
G# for the thumb isn't difficult, because it's just moving up to the next key, but it leaves you in a bad position for the next change. To get to
A C you need to lift the whole hand and go up a fourth. That too may not be very difficult, but it doesn't take advantage of easier moves.
If you make moves using new fingers/adjacent keys, you don't really need to look at the keyboard.
...surprised SimplyPiano would introduce those notes without a lesson on it.
The fingering given by this software application reminds me of software determined guitar tab. Such software probably follows some general principle of numerically smallest movements. But sometimes the results just don't feel right. I think you need to assume such software will give you bad fingerings and you need to develop the judgement to make better choices.
Look for a traditional, classical piano method book that gives scale, arpeggio, and double note fingers in all keys. Study the fingers given and use them as a point of reference to figure out the fingering of passages.