take a look at these ... just to get some ideas of where you can go ... to define your goal ... how many feet up do you want to clear the trunks???

and then just start removing branches from the trunks.. from the bottom up ... say maybe.. one foot per year ... you can always take more in the future.. you cant glue them back on .. lol ...

just be patient ... think in tree time ... if it takes you 5 years.. to get to your goal.. so be it ...

leaves are food making machines ... so dont remove too much of the canopy in any given year ...

dont know where you are.. so i dont know about timing ... and a pic never hurts if you want more specificity ....

ken

ps: i am not sure if i would remove trunks .. that sometimes causes too many new trunk shoots .. and kinda destroys the whole clump.. perhaps someone else can speak to that ...

i hate when i forget the link: https://duckduckgo.com/?q=Heptacodium+miconioides&t=ffcm&ia=images&iax=images

Some lower side branches can be taken when growth starts in spring but I would try to avoid removing any main vertical stems.