Tzitzit that Tore and was Sewn Back

One of the corners of my tzitzis tore off, together with the strings that remained intact. Afterwards, I sewed the corner back onto the garment. Is the tzitzis still kosher, and if not, in what way can I make it kosher again? 

Shalom uVracha,

The tzitzis corner that was torn off and then sewn back on is certainly invalid, due to “ta’aseh v’lo min ha’asuy”.

As for the other three corners:

•  If, at the time the corner was torn off, the garment was left with only three corners, then all the tzitzis must be untied and retied after the garment is repaired and once again has four corners 
• However, if at the time the corner was torn off the garment still had a tzitzis obligation (for example, it was cut in a way that left it with five corners), then even after reattaching the torn-off corner, the tzitzis are not invalidated, and the other corners may remain as they are.