You need to decrease\increase the amount of collected data in Veeam One database.
The current retention policy does not suit your specific requirements.
To modify Data Retention Policy, on Veeam One server run "C:\Program Files\Common Files\Veeam\Veeam ONE Settings\VeeamOneSettings.exe" > General node > Retention Policy Period tab > set the desired amount of months to preserve data for > click Save > Restart Veeam One Monitor and Reporter services.
Starting with version 8 the support utility can be launched from Monitor GUI > Options > Server Settings > Other Settings tab.
Note: In case of decreasing data retention, the change will take effect on the next Saturday's night.
In case of increasing data retention, no historical data will be collected but new data will be collected and preserved in the database according to the new retention policy