also for the purpose of ~
This pattern expresses that an action is done with an additional secondary purpose in mind, meaning 'also for the purpose of ~'.
を兼ねて is used when you do one action that serves two purposes: a primary one and a secondary one. It is often used in spoken and written Japanese, but it has a slightly formal nuance. For example, you might go to a city for sightseeing (main purpose) and also to visit a friend (secondary purpose). In that case, you can say '友達訪問を兼ねて' meaning 'also for the purpose of visiting a friend'.
When using with a verb, attach を兼ねて to the ます-stem: for example, 散歩を兼ねて (with the purpose of also taking a walk). When using with a noun, place を兼ねて directly after the noun: for example, 宣伝を兼ねて (with the purpose of also advertising). The main action comes after this phrase.
This pattern is often used to report one's own intention or to describe someone's action. It can be slightly formal but is common in everyday conversation as well, especially in set phrases like 散歩を兼ねて.