Have a look through the many Sailrite YouTube site. It has everything you need to know; its a great site with everything from simple sail repair to making your own sails. Also many other projects.
Not sure what sail repair task you have but there are sail repair tapes which work ok depending on the issue
www.roadtechmarine.com.au/white-sail-repair-tape/p/TSC220?gclid=EAIaIQobChMI3eP28I3s8AIV4ZVLBR3WkAngEAAYAiAAEgJRoPD_BwE
Of course as above if the repair is significant then a sailmaker is the only solution.