Could not index event to Elasticsearch..cluster currently has [1000]/[1000] maximum shards open

I have an Elasticsearch cluster with single node. Metricbeat and Filebeat are creating daily new index. The ELK Stack have been working properly from last few months. But from today I am getting the below error:

[2020-08-27T10:48:17,387][WARN ][logstash.outputs.elasticsearch][metricbeat] Could not index event to Elasticsearch. {:status=>400, :action=>["in>nil, :_index=>"postgresql-2020.08.27", :routing=>nil, :_type=>"_doc"}, #<LogStash::Event:0x7ba78919>], :response=>{"index"=>{"_index"=>"postgres7", "_type"=>"_doc", "_id"=>nil, "status"=>400, "error"=>{"type"=>"validation_exception", "reason"=>"Validation Failed: 1: this action would add ards, but this cluster currently has [1000]/[1000] maximum shards open;"}}}}

I have gone through other questions asked on the same issue, the suggested solution was to increase the number of data node. But in my case as of now I can't increase number of data node. What can I do to solve this issue? (In my case, every index has single primary shard).

Any help will be appreciated.

If you have a long retention period, switch to weekly or monthly indices. Otherwise consolidate indices and/or reduce the retention period.

Thanks @Christian_Dahlqvist for your reply.
As of now it is urgent to solve this issue. I think to modify the retention period in ILM policy will take some time for me as I am new in ELK stack. Can you please tell or provide some resource on how to consolidate old indexes ? How many index I can consolidate together or is there any size limit in the consolidation of old indexes into a big index?