The general theory of relativity (GR) plays the key role in understanding the nature of spacetime
around us. GR has been successful in demonstrating the fundamental characteristics of gravity through
its appreciable originality and mathematical magnificence. But, despite its success in explaining several
observations, GR is incomplete because of the presence of singularities where all the laws of physics
break down and its inadequacy to explain the dark sector. Under this scenario, it is essential to search
for alternate theories of gravity which are able to address some of the issues in GR. In this work
we investigate the prospect of the string inspired Einstein-Maxwell-dilaton-axion (EMDA) gravity in
explaining astrophysical observations. Studying such a theory is important as it plays a pivotal role in
inflationary cosmology and in explaining the accelerated expansion of the present universe. The charged,
rotating, black hole solution of EMDA gravity corresponds to the Kerr-Sen spacetime which is endowed
with a non-zero dilaton charge, otherwise absent in Kerr black holes arising in GR. From the observed
high frequency QPOs (HFPQOs) in five black hole sources (e.g GRO J1655-40,XTE J1550-564,GRS
1915+105,H 143+322,Sgr A*), we aim to decipher if they posses such a non-vanishing dilaton charge.
In this work, we consider eleven models aimed to explain the HFPQOs.The model dependent QPO
frequencies are compared with the observations and constraints on the dilaton charge are reported with
respect to all the eleven models.