STEP 1 - WHEN CONNECTED TO YOUR WORK WIFI NETWORK...
- Create a new profile in Tasker
- Set the Wifi Connected State condition
- Write the name of your work wifi network
- Accept this and create a new task
STEP 2 - ...SEND A MESSAGE
- Add a Touchless Chat Send Message action
- Set the contact name to the contact you want to send the message to
- Set the message text you want.
- Accept and back out of Tasker to save
Every time you connect to the specified wifi network a message to the contact you selected will be sent.

Send message when you arrive at work
Learn how to send a message to one of your contacts when you arrive at work