First, ensure that the TV is set to the TV (either NTSC (analog) or ATSC (digital)). To do this, press the Source button until this is the highlighted source. (The Source button is the second from the left (as you face the set) on the top of the TV. There is also a source button on the remote above and to the right of the arrow keys.) Next press the Menu button (center of the arrow keys on the remote or the button just to the right of the Source button on the TV). Use the navigation arrows to navigate the menus. The Channel up/down buttons mimic those arrow keys on the remote. Press the Volume Up or right arrow to select an item. Next select Setup and go to Preset. Select this sub-menu and go to Reception. Select the item and then set the mode to TV for over-the-air. Set this to CATV for cable on the antenna RF input. Press Menu repeatedly to go back in the menu system. Return to the Preset section of the Setup menu. Navigate to the Auto Install and select this. Wait for the TV to scan all channels for either NTSC or ATSC depending on the current Source. Exit the menu and change the source to the other TV tuner. Repeat the steps to Auto Install to store channels for both the analog and digital tuners.
The manual is available from ManualsLib here: https://www.manualslib.com/manual/101765/Memorex-Mlt1912.html
. See pages 5, 16 and 17 (pages 6, 17 and 18 as labeled by ManualsLib) for the screen shots and pictures of the remote control and front panel buttons for these steps.
Since there are only a few low-power NTSC stations still broadcasting, you may not find any stations when you scan for channels with NTSC as the source. Depending on the stations in your area, skipping the Auto Install step for NTSC may be appropriate. I hope this helps.