Tablejacks work by stabilizing to the three stationary table glides.
Side to side movement
If the table rocks from side to side (or sideways from the tablejack), hold the table top from the under side with hand, press down the tablejack lever, lower table until it stabilizes on the other three glides and release lever.
Front to back movement
If the table rocks towards the tablejack, slightly lift the table from the tablejack side, step on the tablejack lever, lower the table down until it stabilizes on the other three glides and release lever.
If table is still not stable, repeat steps listed above.