Use Modify|Apply Patch to apply a patch file to your working copy. Currently supported patch file formats are unidiff patches. See Create Patch on how to create patches with SmartSVN.
For the Select Patch File dialog, select the patch file which you want to apply. Typically, patch files have .patch or .diff extensions. Based on the file paths contained in the patch file, SmartSVN will try to detect the correct base directory to which the patch should be applied. It will fail, if at least one file to patch has not been found in the working copy.
The resulting window is similar to the Merge Preview window, refer to this section regarding the available commands. The Files area allows to deselect certain files from the patch. You can finally perform the patching by Patch|Apply Patch.
In case the patch could not be applied to certain files, an Unpatchable files area will be displayed in the top of the window. The table contains the Path of the file and a description of the Problem. The tooltip text of the Problem column contains more details in case expected and actual lines did not match when trying to apply the patch to the file.