A study reload would be to reload the entire study.
This would mean that to do a study reload, you would need a study archive (in a zip format) to reload into your existing study. To obtain a study archive, this would require you to export your study as explained here: https://www.labkey.org/Documentation/wiki-page.view?name=studyReload#manual
If you have Excel files for those datasets, then what you'll need to do is:
1. Export your existing study (https://www.labkey.org/Documentation/wiki-page.view?name=exportStudyFolderObjects
2. Unzip the study archive
3. In the unzipped archive, there should be a study folder within it and a datasets subfolder. If you access that datasets subfolder, you should see various TSV files for your datasets, such as "dataset5001.tsv". The number corresponds with a specific dataset in your study. You will want to identify your specific dataset that you wanted to reload with that Excel data and then replace the information within that specific TSV file with the same data in your Excel spreadsheets. Ensure that you maintain the tab-separated format and that the column headers remain untouched. If the data ends up malformed in the TSV file, the import will fail.
4. After you replace the data in the TSV file, zip up the study archive.
Since this is your first time doing this, I would recommend testing it first.
1. To ensure that you've zipped this study archive up properly, try to create a new study folder and import that zip into your new study folder. If the zip archive was setup properly, it should create a new study with the revised data. (https://www.labkey.org/Documentation/wiki-page.view?name=studyImport
2. If everything was successful, delete the test study you created and then use that archive to reload your study with.
For details on the study archive design, please see https://www.labkey.org/Documentation/wiki-page.view?name=studySerializationFormats