Setting the output pin drive current sets the “Current Strength” option for the desired pin in Quartus II.

Devices that support the Current Strength option are APEX II, Arria series, Cyclone series, HardCopy series, MAX II, and Stratix series.
 
The setting method is as follows.
1. Launch Assignment Editor. (Click Assignments menu ⇒ Assignment Editor)
2. In the To column, enter the pin name for which you want to set the output current.
3. Select "Current Strength" from the Assignment Name field.
4. Select the desired current value from the Value column.
5. Save your settings. (File menu ⇒ Save)
 
Then compile for the settings to take effect. Also, after compiling, check the compilation report to confirm that the Current Strength option has been applied.

For details, refer to the Elsena document Quartus II Beginner's Guide - How to Set Commonly Used Logic Options (Individual Settings).

The support range for the settable output current value varies depending on the pin's I/O standard and pin arrangement (top/bottom, row/column). For details, please check the I/O Structure “Programmable Current Strength” (or Current Strength, Programmable Drive Strength) in the datasheet of each device.