Please tell how to adjust the top tension of MC11000. while doing embroidery a nest is formed at the bottom.

it is so easy it is the tension icon (look in your manual) that is visible where ever you may be in the machine, it looks like 2 threads twined together in a loose knot. i always recommend totally un-threading upper and lower, cleaning out entire bobbin area, then re-threading and maybe a new needle when this happens. it is usually not a tension issue, but rather a dust/dirt issue.