Iīve flown the approach and this is what I understand.
The lowest altitude at which you can fly the holding pattern is the transition level (thatīs why it says "trans level" in the plan view, inside the holding), however, you normally enter the hold at a higher FL due to other A/C flying the approach or already holding. As the A/C flying the approach lands or reports a missed, the following A/C is cleared for the approach. At that time every A/C holding is cleared to descend 1,000 ft (thatīs why it says "FL by ATC". ATC assigns FLs to maintain while holding.
Do you travel to Argentina ?
What A/C do you fly ?