This small hack will allow you to delete a large amount of data just by running it.

Script for deleting a large number of entries in the Salesforce

//guide:
//1) login to salesforce
//2) open dev tools console
//3) execute "pre-start script" in dev tools console
//4) in "useful script" replace ObjectApiName to your object name
//5) execute "useful script" in dev tools console

//pre-start script
document.write('<script src="/soap/ajax/44.0/connection.js" type="text/javascript"></script><script src="/soap/ajax/44.0/apex.js" type="text/javascript"></script>')
var __sfdcSessionId = document.cookie.split('; ').find((item) => {return item.indexOf('sid=') == 0}).substring(4)

Script for records deleting

//useful script
var callDeleteFunction = function(){
    var records = sforce.connection.query('SELECT Id FROM ObjectApiName LIMIT 200')
    var recIds = []
    if (records.records) {
        for (let rec of records.records) {
            recIds.push(rec.Id);
        }
        sforce.connection.deleteIds(recIds,(result) => {console.log('ok');callDeleteFunction()})
    }
}
callDeleteFunction()