Here's the completed conversation using "shall," "will," or the correct form of "be going to":

A: Your garden needs tidying.
B: I know I **am going to** do it this afternoon.
A: **1)** **Shall** I lend you my gardening tools?
B: Thank you. I **2)** **will** come round to collect them later.
A: **3)** I **am going to** visit my brother this afternoon, so I **4)** **can** bring them to you now if you like.

Feel free to ask if you need further help!