Once you solve the First scarab puzzle do not use the switch. If you do it, you will raise the water level and you will not be able to use the ankh symbol for the Relic. Instead, climb up the ladder and jump to grab the handhold of the statue's arm as usual.

Traverse around the arm and stop after the 3rd corner. Press the down direction key and jump backwards.

Lara will land on the arm of the other statue and you will reach the level where the Second scarab puzzle is. Solve the puzzle to open the gate (A) but do not use the switch now. Instead, drop down to the ledge on the right and go for the ankh symbol that opens the gate to the Relic, as you would normally do (B).

(Note: If you are during the Time Trial process, ignore the ankh symbol for the Relic and use the switch to raise the water level.)

Once you open the gate to Relic, climb up the first statue again until you reach the First scarab symbol. Do the shortcut once more to reach the Second scarab symbol and use the switch to raise the water level. Then proceed as usual.