The Vernier Sensor Block for MINDSTORMS EV3 software does not have a Zero function. You can easily create a correction in your program to effectively zero the sensor reading:

1. Determine what the sensor is reading when it should read zero. This is the offset value.
2. Insert a Math block to correct the value by that amount.
3. Select the subtraction setting on the Math block and enter the offset value into the b box in the Math block.
4. Wire the Numerical Value of the sensor reading into the a box.

The Vernier sensor block for EV3 MINDSTORMS can be found here:

LEGO® MINDSTORMS® Education EV3 Core Set with Charger (LEGO-EV3-CORE)
NXT Sensor Adapter (BTA-NXT)
Vernier Engineering Projects with LEGO® MINDSTORMS® Education EV3 (EP-EV3-E)
LEGO® Mindstorms® EV3 Troubleshooting and FAQs