In the time of some of the Imams (A), it seems some of the Shi'a were in this situation also, because advice to them on how to commemorate Ashura comes across sometimes as individual advice.

Even though gathering to mourn Imam Husayn (A) is recommended, and spiritually beneficial, it is not a requirement to attend a specific kind of gathering, and sometimes it is not possible for one reason or another. 

So, for instance, you can recite ziyarat to Imam Husayn (A), abstain from worldly activities (as much as is possible), recall what happened on Ashura, wear black, be serious, and engage in private mourning.

Sometimes there is a special sincerity in commemorations that are done alone, because there is no risk of doing them for show or just to do what everyone else is doing.

It is nice, however, if you can share it with someone, ideally in person, or at least virtually.

This is assuming that you do not live with other people who would be willing to commemorate; it is good if you can do a household commemoration, although sometimes that is not an option for some people. 

In the end, Imam Husayn (A) died alone on the battlefield, and one can also use the opportunity to empathize with that.