The standard factory tension setting is usually the midpoint of the dial. If your tension setting ranges from 1 to 10, the most usual setting would be 5. From that point, you would either tighten or loosen based on how it is stitching with the needle you are using, the thread type, and the fabric thickness.

The upper tension setting should be something you are comfortable adjusting as not all fabric, thread, or needles stitch the same. Righty-tighty, or lefty-loosey.

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You probably wont find it listed anywhere as it is from experience and changes with different material thickness and needle size
SO how to set tension
thread the machine and adjust the tension until you feel a drag on the thread
now thread the needle and sew a piece of scrap material
if the thread bunches up underneath then increase the thread tension until it sews properly
if the bottom thread is pulled to the top or the thread keeps breaking loosen ti off a bit
when the stitch is being properly formed , both bottom and top threads should meet at the center of the two materials being sewn