How do you adjust the wiper arm on a 1991 Montero This is in regards to the position of the blade on the windshield?

The wiper arm should have a removable cap at the lowest pivot point where the arm meets the firewall/hood level. With the cap removed there should be a 10-12mm nut exposed that requires loosening and removal to slip the arm off the grooved spindle and re-mount to the readjusted/desired coverage area. Re-tightened once adjusted to to avoid slippage while in operation.