internal static XNamespace w = "http://schemas.openxmlformats.org/wordprocessingml/2006/main"; 
 
internal static void ImportTableStyles(string sourcefilepath, string destinationfilepath)
        {
            using (var repeaterSourceDocument = WordprocessingDocument.Open(sourcefilepath, true))
            {
                XDocument source_style_doc;
 
                var repeaterSourceDocumentPackagePart = repeaterSourceDocument.MainDocumentPart.OpenXmlPackage.Package.GetPart(new Uri("/word/styles.xml", UriKind.Relative));
 
                //Get styles.xml
                using (TextReader tr = new StreamReader(repeaterSourceDocumentPackagePart.GetStream()))
                    source_style_doc = XDocument.Load(tr);
 
                var tableStylesFromRepeaterSource = source_style_doc.Descendants(w + "style").Where(x => x.Attribute(w + "type").Value == "table").Select(x => x).ToList();
 
                using (var targetFileToImportTableStyles = WordprocessingDocument.Open(destinationfilepath, true))
                {
                    XDocument dest_style_doc;
 
                    var destpart = targetFileToImportTableStyles.MainDocumentPart.OpenXmlPackage.Package.GetPart(new Uri("/word/styles.xml", UriKind.Relative));
 
                    //Get styles.xml
                    using (TextReader trd = new StreamReader(destpart.GetStream()))
                        dest_style_doc = XDocument.Load(trd);
 
                    //Add all the style elements from source document styles.xml 
                    foreach (var styleelement in tableStylesFromRepeaterSource)
                    {
                        if (!dest_style_doc.Elements(XName.Get("styles", w.NamespaceName)).Any(x => (string)x.Attribute("styleId") == (string)styleelement.Attribute("styleId")))
                        {
                            dest_style_doc.Element(XName.Get("styles", w.NamespaceName)).Add(styleelement);
                        }
                    }
 
                    //Save the style.xml of targetFile
                    using (TextWriter tw = new StreamWriter(destpart.GetStream(FileMode.Create)))
                        dest_style_doc.Save(tw, SaveOptions.None);
 
                }
            }
        }

http://www.adigopula.co.uk/post/Importing-Table-Styles-in-Word-Document-using-OpenXML-sdk.aspx

After importing tables from source document to target document, use this snippet to import table styles missing in the target document to enable correct formatting of the table.

Imorting Table styles in word document using OpenXML Sdk

C#