Fill in the blank with the most appropriate option
 

I will write a letter to you tentatively ______ the dates of the programme. 

Indicating 

The most appropriate word to fill in the blank is indicating.

The other options are not as accurate. Involving suggests that the letter will include the dates of the program, but this is not necessarily the case. Urging and guiding suggest that the letter will try to persuade the recipient to attend the program, but this is also not necessarily the case. Indicating is the best option because it suggests that the letter will simply mention the dates of the program, without any further elaboration.