If it's still working you can use a drop of RTV sealant and then heat shrink tubing. I did it to my work phone cable and its perfect. https://www.google.com/shopping/product/14208702255767148224?q=white+rtv+silicone&client=ms-android-att-us&sa=X&biw=360&bih=612&tbs=vw:l,ss:44&prmd=sivn&prds=epd:1430137406172427887,paur:ClkAsKraX_lzAbYUHapb6xGc5wG-uuLm4vnQAh-ysapO-LwLL5TiZBOzWVxSKTiLypknlumKSW-AxkjZbVggmNA3mbW2QHfs7jEA96NIw52xN8zqt9Fl86kTrxIZAFPVH73w9GC269wv1awJ5I6RvyAQTP4Nww,cdl:1,prmr:1,cs:1&ved=0ahUKEwi75M_1v5zeAhVL11MKHRecAtkQgTYIgwU
https://www.acehardware.com/departments/lighting-and-electrical/cable-management-cable-ties-and-electrical-tape/heat-shrink-tubing/3428851
Those are generic links. But that's what you want to use.