Hi @annyreddy
I am able update asset meta data title using below code. check whether required permission is set for the service user which you are using.
Resource metaResource = resourceResolver.getResource( "/content/dam/we-retail/en/products/apparel/gloves/Gloves.jpg/jcr:content/metadata");
ModifiableValueMap modifiableValueMap = metaResource.adaptTo(ModifiableValueMap.class);
modifiableValueMap.put("dc:title", "Title After Update");
if(resourceResolver.hasChanges()){
resourceResolver.commit();
}
Asset Before Update (with title configured) :

Asset After Update (using service resource resolver in backend) :
Hope this helps!