What to do when you found something new, but don’t have motive/application to justify it?
This is hard to answer without more information about the actual problem, but in general it is all about finding the correct publication venue. It does not necessarily mean a venue with lower impact, but one with another focus.

If you really can not think about any practical application, it might still solve an interesting problem and might find an application in other areas.

For example, it might be the case that you found a new method to formulate process scheduling as a graph problem that you can solve in an interesting way. The resulting schedules might not be better than the state of the art scheduling algorithms, so you get rejected by journals about process scheduling. Still it is an interesting graph problem so it might be better suited for journals with the focus on  graph theory.

But the most important aspect in this context is to tailor the paper to the publication venue. If you now try to submit to the graph theory journal do not write "This paper presents a method to improve process scheduling" but "This paper presents an efficient method to solve the minimum dominating set problem under the constraint .... It has, for example, application in the area of process scheduling".