There are two ways to mirror a part in Solidworks:

1. Using the Mirror Part Command which creates a new derived part file.
2. Using the Mirror Command to store the mirrored part in a new configuration in the same file.

Method 1: Using the Mirror Part Command

1. Select the plane of symmetry along which you want to mirror your part. It can either be a SolidWorks plane or a flat surface on the object.
2. Go to Insert -> Mirror Part. (Tip: Selecting a plane is necessary to make the Mirror Part command visible.)
3. Under Transfer, select the items that you want from the source part to be included in the derived mirror part. Or you can also select everything just to make sure the mirror part file contains all the data of the original file.
4. Optionally, If you want to make edits or keep working on the original part and don’t want to reflect those changes in the derived part, then under Link, click “Break link to original part”. And additionally, under Visual Properties select Propagate from the original part to maintain all your appearances from the original part.
5. Click on the Green Checkmark and the mirrored part will appear. You can now save this new part file for further use.

Method 2: Using the Mirror command

1. Before we apply the Mirror command, we need to create a New Configuration. In the Feature Manager tree area, navigate to the Configuration Manager tab. Right-click and select Add Configuration.
2. Give this new configuration a suitable name and description. Optionally, under Advanced Options, you can deselect Suppress new features and mates if you want to add additional features to the original configuration and don’t want those features to be suppressed in this mirrored configuration. Click Green Checkmark.
3. Now we’ll perform the mirror operation. Mirror command can be accessed in multiple ways: Either from Features Tab-> Mirror or from Features Tab-> Linear Pattern-> Mirror or from Insert-> Pattern/Mirror-> Mirror. (Tip: If you’re ever stuck and can’t find a command, you can always search for that command in the search bar present in the top-right corner of the SolidWorks window (make sure to switch the help box from Solidworks help to Commands before searching by clicking on the drop-down arrow present in the box))
4. Select the symmetry plane in the Mirror Face/Plane box and in the Bodies to mirror box, select all the bodies that you want to mirror. Under options, make sure to deselect Merge solids or Knit surfaces as we’ll be deleting the original body.
5. To delete the original body, select Delete/Keep Body from the Direct Editing tab. (Tip: If this tab is not visible, right-click on the Features tab and select Direct editing present in Tabs.) Also available in Insert-> Features-> Delete/Keep Bodies.
6. Select the original body/bodies and while making sure the Delete Bodies option is selected, click Ok. (Tip: You can either select bodies by clicking on the bodies in the graphics area or by expanding the Solid Bodies folder in the feature tree and then selecting the bodies.)
7. Now you have the mirrored part. To go to the original part Double click on the Default configuration in the configuration tab.