Choose the correct word to complete the sentence. I will write a letter to you tentatively_____________ the dates of the programme.

The correct word is indicating.
'Indicating' means 'indirectly or briefly mentioning.' 'I' will write a letter here that addresses the programme dates (briefly). This term completes the sentence's context.
'Involving' means 'including as a necessary or important aspect or outcome.'
'Urging' is defined as "persuading people to accomplish something."
'Guiding is a direct or indirect influence on the action or growth of.'