There are different ways to re-establish the WiFi connection.
Method 1 : Using Computer itself
Download and re-run the printer software from here --> http://gdlp01.c-wss.com/gds/6/0100005316/01/mast-win-mx450-1_0-ucd.exe
Open/Run the downloaded printer setup file and follow the onscreen instructions to install the printer. And install the printer as a new printer like you did when you first setup this printer.
Method 2 : Using Printer itself
1. Press the Setup button on the printer.
2. Use the arrow keys to select Drive Settings and press OK.
3. Select LAN Settings and press OK.
4. Choose Wireless LAN Setup and press OK.
5. If a WPS prompt appears, press the STOP button or cancel that.
6. Select Standard Setup and press OK.
7. Select your WiFi network that your computer connected to and press OK. When entering the passphrase/password ***** WiFi, use the Tone or Star (*) key to change character modes (upper case, lower case and numbers)
Once you connected it to your WiFi network, you have to add it to your computer again. To do that, follow the steps below
On your computer, press Windows and R keys and this will bring Run. Type control printers and press enter. From the resulting screen, click Add Printer button and follow the onscreen instructions to add the printer.
If you have any difficulty on following the steps above, please let me know and I will walk you through it. Only rate the answer after we solved the problem.