The correction method differs depending on the calendar reading target (PLC or V/TS).
For the reading target, check the following setting.

Setting location:
V-SFT editor [System Setting] → [Unit Setting] → [SRAM/Clock] → [Use Built-in Clock]

Checked .... Clock built in the V / TS used
Unchecked .... Clock built in the PLC used

For more information about the correcting method, click here.