The reaction force in the plate is due to the interactions of the rigid plate with the deformable body. In Workbench LS-DYNA, you can define a body contact tracker and scope it to the rigid plate before running the analysis. Next, you can define a Contact Force tracker (see screenshot below), and then select the proper contact region and orientation. This should provide you with the reaction forces on the moving plate.
As a side note, under Analysis Settings, make sure your desired frequency at which the histotry data is reported is specified under Time History Output Controls.
Finally, if you have access to Ansys Learning Hub (ALH), the following course on Ansys Workbench LS-DYNA might be of interest to you: SuccessFactors Learning: Item Details for Ansys Workbench LS-DYNA Getting Started (plateau.com)