The CT-90326 remote was included with several Toshiba televisions, including the 42HL800A. You can't directly scan for channels with a single button on the remote. First make sure that the TV is set to the TV input. (Use the Input button on the remote (top left) or the TV (lowest button on the left side as you face the screen).) Next press Menu (the second lowest button on the TV or the button at the lower left of the Left arrow button). Use the Left or Right arrows to select Setup (with the gear icon) and press OK. Use the Up/Down arrows to select Auto-Tuning and press OK. Use the Up/Down arrows to reach the line to select the type of channels to search for a signal. Then use the Left/Right arrows to select Digital channels, Analog channels or both. Go down another line to set the bandwidth of your broadcasts. Again use the Left/Right arrows to select the correct one. Go down one more line to Start Scan and press OK.
These details are in the manual for your TV. The manual for the 42HL800A is available from Toshiba's product support download page: http://www.mytoshiba.com.au/support/televisions/led-backlit-tv/hl800a/42hl800a/download . The direct link to the manual is http://www.mytoshiba.com.au/file/download/resource/file/19610/toshiba_32av80032%2040lv80026%2032el80032%2042hl800_om%20(au).pdf
I hope this helps.