Administration > Tools > Batch update > Search and replace.
Settings: Search method: Whole words only Case insensitive: tick (unless you are confident in case in question. Search text/pattern: engag Replacement text: This will vary depending on the result. Case-sensitivity can not be applied to the replacement, so if you find Engag you will need to replace with Engagement; find engag, replace with engagement. Alternatively, don’t tick Case insensitive and search first for Engag with the upper case replacement; then again for engag with the lower case replacement.