Can you let me know how many times can a root canal tooth be retreated?

Varies with the case: Root canal retreatment can be a successful procedure. The success depends on correcting the deficiency with the prior treatments. What happes all too often though, is a tooth becomes more structurally compromised when not managed appropriately during root canal therapy. If there are structural concerns, it may be worth getting opinions on salvageability from your dentist or endodontist.

As few as possible: Each time the procedure is done there is a degree of risk. When re-done this increases the level of risk. I would have a root canal procedure done by a reputable dentist who has the best chance to do this correctly the first time. Secondly, the back teeth need a crown following the root canal procedure. Thirdly, if there is grinding or wear, i would obtain a professional night guard.