Note: The following screenshots are taken when LQB is on Liquefy mode, but these steps ara applicable when it's on Idle mode.
1) Go to the Liquefier page.
2) Read the PT503B value (Dewar pressure) and remember it for a few seconds.
The goal is to set the Dewar Set pressure +0.5psig than this PT503B value to temporarily turn ON heaters and get rid of the blocking alarm.
3) Go to the Settings page of the Liquefier, and tap the "Dewar Pressure Setpoint" field.
4) Enter the set pressure value (PT503B + 0.5 psi: for example in this case it should be something like 7.1 psi) using the keypad that appears in the lower-right corner of the screen. And don't forget to press the enter button on that keypad. And then navigate to the Liquefier screen (Fig in step 2).
5) You will see that the heaters on cold-heads are ON (blinking orange indicators) with the Dewar pressure low alarm for a few seconds and those will disappear in few seconds.
6) When the blocking disappears, change the "Dewar Pressure Setpoint" back to the original (previous) value using step (3).
7) Wait for some time, and If the Blocking happens again, you can try this again.
8) If the same thing happens again and again, then it sounds the Liquefier needs to be cleaned (use LHe Dewar cleaning procedure for that).