Hi and welcome to Just answer.
Initially, try to open your machine face cover to access the needle mechanism. Look at the shaft and if it is bent you have to replace the shaft. If not look at the shaft screw if it is loose try to tighten it.
If you are using zigzag or embroidery before the needle shaft is not came back to home position. You need to lubricate the mechanism use the aerosol spray for sewing machine then go back to zigzag mode and test it with few stitches then try to back in straight stitch.
Hope this information will be helpful.
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the shaft is not bent. it has a spring pulling it to the left. I don't see how to adjust it.
Can you please give a screen shot of that particular area?
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